Fan-fold shielded electrical leads

ABSTRACT

Fan-folded electrical leads made from copper cladded Kapton, for example, with the copper cladding on one side serving as a ground plane and the copper cladding on the other side being etched to form the leads. The Kapton is fan folded with the leads located at the bottom of the fan-folds. Electrical connections are made by partially opening the folds of the fan and soldering, for example, the connections directly to the ground plane and/or the lead. The fan folded arrangement produces a number of advantages, such as electrically shielding the leads from the environment, is totally non-magnetic, and has a very low thermal conductivity, while being easy to fabricate.

The United States Government has rights in this invention pursuant toContract No. W-7405-ENG-48 between the United States Department ofEnergy and the University of California for the operation of LawrenceLivermore National Laboratory.

This is a Division of application Ser. No. 08/039,671 filed Mar. 30,1993 now U.S. Pat. No. 5,375,321.

BACKGROUND OF THE INVENTION

The invention relates to the fabrication of electrical leads,particularly to shielded electrical leads, and more particularly tofan-fold shielded electrical leads and a method for fabricating same.

Electrical leads are formed on substrates for various applications andnumerous configurations, including multi-layer assemblies, have beendesigned and fabricated. These designs include approaches for shieldingthe leads from the environment, both physical and electrical as well asproviding flexible substrates on which leads are formed. One of theproblems associated with the design of electronic components is"cross-talk" among the components, and thus shielding has become a majorconcern. As the electronic technology develops, in addition to the needof electrical signal leads to be electrically shielded from theenvironment, including other signal leads, there in a need for suchelectrical leads to be non-magnetic, have very low thermal conductivity,be vacuum compatible, bakeable, compatible with cryogenic temperatures,designed for multiple signal applications, while being easy tomanufacture and thus inexpensive. In addition, such signal leads must insome instances be suitable for high voltage applications. While theprior known designs and fabrication techniques have resulted insatisfactory electrical signal leads for certain of these needs, suchare often expensive and/or have certain limitations for use in certaintypes of applications. Thus, there is a need for electrical signal leadswhich can satisfy the above-identified requirements, and which can alsobe fabricated inexpensively. The fan-fold shielded electrical leads ofthis invention meets all of the above-mentioned needs, and in additionpermits easy connections to be made to the signal leads at any point (ormultiple points) along the length of the signal leads. In addition, theshielded electrical leads of this invention are suitable for handlingvoltages in excess of 1000 volts.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method offabricating electrical leads having physical and electrical shielding.

It is a further object of this invention to provide multiple electricalleads which are shielded, non-magnetic, have very low thermalconductivity, are vacuum and cryogenic compatible, and are bakeable.

A further object of the invention is to provide fan-fold shieldedelectrical leads, which has the capability for uses with voltages inexcess of a 1000 volts.

Another object of the invention is to provide a method for fabricatingfan-fold shielded electrical signal leads.

Other objects and advantages of the invention will become apparent fromthe following description and accompanying drawings.

Basically, the invention involves shielded electrical leads and a methodof fabricating same, whereby the electrical leads are shielded bothphysically and electrically, while being vacuum and cryogenictemperature compatible, being totally non-magnetic while being bakeable,having a very low thermal conductivity, and suitable for multiple signaland/or multiple layer applications. In addition, the shielded electricalleads of this invention are suitable for voltages in excess of 1000volts. More specifically, the above-identified advantages of the presentinvention result from a fan-fold shielded electrical lead assembly whichis easily fabricated and may effectively use any number of electricalleads. The method of fabrication is carried out by simply etching awaycertain areas of a double cladded substrate to form electrical leads onone side and fan-folding the substrate such that the electrical lead areat the bottom of each fan-fold, thus providing maximum shieldingtherefore.

The leads can be readily connected by soldering, for example, electricalconnections thereto, after partially opening the fan-folds.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a partof the disclosure, illustrate an embodiment of the invention and,together with the description, serve to explain the principles of theinvention.

FIGS. 1-3 illustrate in cross-section various fabrication steps forfabricating the fan-fold shielded electrical leads of this invention,with FIG. 3 illustrating in cross-section an embodiment of the completedshielded electrical lead assembly.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is divided to fan-folded electrical leads and amethod for fabricating same. Basically, the invention is made from adouble clad substrate with the cladding on one side of the substrateserving as a ground plane and the cladding on the other side is etchedto form the desired leads, whereafter the substrate is fan-folded suchthat each lead is located at the bottom of a fold so as to provideshielding on both sides of the leads.

Electrical connections are made directly to the leads or to the groundplane by partially opening the fan-folds and soldering or otherwisesecuring the connections, whereafter the fan-folds may be reclosed ifdesired. This invention provides one or more electrical leads that areelectrically and physically shielded from the environment, totallynon-magnetic, has very low thermal conductivity, is vacuum compatible,bakeable, compatible with cryogenic temperatures, and designed suitablefor single and multiple signal leads, while additionally being easy tomanufacture.

While the following description and accompanying drawings set forth anembodiment of the invention made of double-clad copper with two (2)leads, such is for illustration purposes, since the fan-fold arrangementmay utilize a single lead or multiple lead and be made of any suitableconductive double-clad material. By way of example, during experimentalverification of this invention, nine (9) fan-folded leads were formed ona single substrate. It is also recognized that the lead bearingsubstrates can be connected together to form any desired number of leadson a single assembly.

The fan-fold shielded electrical lead assembly illustrated in FIG. 3 isfabricated from copper-clad Kapton. As shown in FIG. 1, the copper onone side of the substrate 10 is retained as a ground plane 11, and thecopper on the other side is etched away to form signal leads 12 and 13.The technique for etching the copper is well known, and is exemplifiedby selectively covering the copper-clad surface with adhesive tape andimmersing in a saturated aqueous solution of Ferric Chloride. Theuncovered portion of copper cladding is etched away in typically 20minutes (longer if the solution is not saturated), exposing the inertsubstrate, and leaving behind the copper cladding in those regionscovered, or masked, by adhesive tape. For example, the leads 12 and 13are 1/16 inch wide, spaced 1/2 inch apart, using 0.005 inch thick Kaptonthat has been clad with copper on both sides. The thickness of thecopper is 1/2 oz/square foot, or 0.0007 inch thick, on both sides of thesubstrate 10. Kapton is a Trademark for polyimide material, specificallya polypyromellitimede, manufactured by E. I. duPont deNemour and Co.,Inc.

The thus etched Kapton substrate 10 is then folded lengthwise in afan-fold, as illustrated in FIG. 2, leaving the leads 12 and 13 locatedat the bottom of grooves or bends 14 formed by sides or surfaces 15 ofthe substrate 10. Whereafter the sides or surfaces 15 of substrate 10are pressed flat forming fan-folds 16, as shown in FIG. 3, providingmaximum shielding of leads 12 and 13 between the sides or surfaces 15 ofthe Kapton substrate 10. Maximum shielding is achieved because the leads12 and 13 are almost totally surrounded by the ground plane 11.

Electrical connected to leads 12 and 13 can be made along the lengththereof by partially opening the fan-folds 16 of the assembly of FIG. 3and soldering or otherwise electrically connecting wires or the like tothe leads 12 and 13 and/or to the ground plane 11, as needed. Whereafterthe fan-folds 16 may be repressed flat.

As pointed out above, the fan-fold assembly of FIG. 3 may be constructedwith a single lead or with multiple leads, and if desired, the assemblyof FIG. 3 can be mechanically and electrically connected to anotherdouble-clad assembly having leads formed on one side thereof. Whiledouble-clad copper has been described, other electrically conductivematerials such as gold, silver and aluminum may be double-clad on anappropriate flexible substrate, provided the substrate and cladding canbe readily bent to form the fan-folds without damage to either thesubstrate or the ground plane. In addition to the Kapton (polyimide)substrate, other dielectric materials may be used as the substrate, suchas polyester (Mylar), polytetrafluoroethlene (Teflon), polyethylene,cellulose acetate, polystyrene, fiberglass, fiberglass composites, andpaper.

While the fan-fold shielded electrical lead assembly constructed ofexemplified copper-clad Kapton, as described above, the transmissionline impedance of each signal lead was measured to be 10 ohms, and thecapacitive coupling of one signal lead to the adjacent signal lead was0.016 pF/meter, a vast improvement over conventional flat strip-linegeometries. The fan-fold assembly is suitable for voltages in excess of1000 volts. The thermal and other material properties of Kapton andcopper are well-documented in the literature, and Kapton is recognizedas being non-magnetic, of very low thermal conductivity, is vacuum andcryogenic temperature compatible, and bakeable.

Other electrically conductive and/or dielectric materials can besubstituted in applications of less demanding operating conditions,while retaining the benefits of the fan-fold arrangement. Also, athicker layer of Kapton, or other dielectric, offers higher voltagestandoff and lower capacitance to ground, whereas a thinner layer iseasier to fold.

It has thus been shown that the present invention provides a shieldedelectric signal lead assembly which can be readily fabricated and iscapable of a wide variety of applications, as well as permitting easyconnection to the shielded leads thereof. In addition to beingcompatible with various environments, the fan-fold shielded electricallead assembly is suitable for applications using voltages in excess of1000 volts.

While a specific embodiment and specific materials and parameters havebeen described and/or illustrated to provide an understanding of theinvention, such is not intended to be limiting, as modifications andchanges will become apparent to those skilled in the art. It is intendedthat the scope of this invention be limited only by the scope of theappended claims.

We claim:
 1. An electrical lead assembly, comprising:a substrate; alayer of electrically conductive material on one side of said substrate;a plurality of electrically conductive leads on an opposite side of saidsubstrate; said substrate and said layer of electrically conductivematerial having a plurality of interconnected fan-folds such that anelectrically conductive lead is located adjacent a bottom section ofeach fan-fold.
 2. The electrical lead assembly of claim 1, constructedfrom doublecladded copper substrate, wherein a portion of one side ofthe double-cladding is removed to form said at least one electricallyconductive lead.
 3. The electrical lead assembly of claim 1, whereinsaid substrate is made from a sheet of material selected from the groupconsisting of polyimide, polyester, polytetrafluoroethylene,polyethylene, cellulose, acetate, polystyrene, fiberglass, fiberglasscomposites and paper.
 4. The electrical lead assembly of claim 1,wherein said substrate is made of a dielectric material, and said layerand said lead are composed of material selected from the groupconsisting of copper, gold, silver and aluminum.
 5. Fan-folded shieldedelectrical lead assembly comprising:a sheet of polypyromellitimedematerial; conductive material on one side of said sheet of forming aground plane; conductive material on the opposite side of side sheet ofmaterial forming a plurality of spaced, longitudinally extendingelectrical leads; said sheet of material being folded in a plurality ofinterconnected fan-like configurations such that each of thelongitudinally extending electrical leads is located adjacent a bottomsection of an associated folded section of said fan-like configurations;whereby maximum shielding for each of said longitudinally extendingleads is provided.